U.S. patent application number 10/361772 was filed with the patent office on 2003-06-19 for plasma etching apparatus.
Invention is credited to Hirose, Eiji, Nagahata, Kazunori.
Application Number | 20030111180 10/361772 |
Document ID | / |
Family ID | 27338996 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030111180 |
Kind Code |
A1 |
Nagahata, Kazunori ; et
al. |
June 19, 2003 |
Plasma etching apparatus
Abstract
A plasma etching apparatus includes an upper electrode and a
lower electrode (susceptor) on which a semiconductor wafer is
disposed, the upper and lower electrodes being arranged within a
process chamber, a first high frequency power source for applying a
first high frequency power having a frequency not lower than 50 MHz
to the upper electrode, a second high frequency power source for
applying a high frequency power having a frequency not lower than 2
MHz and lower than the frequency of the first high frequency power
to the upper and lower electrodes. The frequency of the high
frequency power applied by the second high frequency source to the
upper electrode is equal to that of the high frequency power
applied by the second high frequency source to the lower electrode,
and the high frequency power applied by the second high frequency
source to the upper electrode has a reverse phase relative to the
high frequency power applied by the second high frequency source to
the lower electrode. The inner space of the process chamber is
maintained at a predetermined reduced pressure state, and supplied
with an etching gas. The high frequency power applied from the
second high frequency source to the upper electrode permits
increasing the thickness of the plasma sheath formed on the upper
electrode.
Inventors: |
Nagahata, Kazunori;
(Nakakoma-gun, JP) ; Hirose, Eiji; (Nirasaki-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
27338996 |
Appl. No.: |
10/361772 |
Filed: |
February 11, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10361772 |
Feb 11, 2003 |
|
|
|
09697083 |
Oct 27, 2000 |
|
|
|
09697083 |
Oct 27, 2000 |
|
|
|
PCT/JP99/06619 |
Nov 26, 1999 |
|
|
|
Current U.S.
Class: |
156/345.47 ;
156/345.24; 156/345.28; 156/345.43; 156/345.44; 216/71 |
Current CPC
Class: |
H01L 21/31116 20130101;
H01J 37/32183 20130101; H01J 37/32091 20130101; H01J 37/32165
20130101 |
Class at
Publication: |
156/345.47 ;
156/345.44; 156/345.43; 216/71; 156/345.28; 156/345.24 |
International
Class: |
H01L 021/306; H01L
021/3065; C23F 001/00; C03C 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 1998 |
JP |
10-336886 |
Oct 29, 1999 |
JP |
11-308765 |
Claims
What is claimed is:
1. A plasma etching apparatus, comprising: a process chamber in
which a target object to be processed is housed; exhaust means for
maintaining a predetermined reduced pressure within said process
chamber; gas introducing means for introducing an etching gas into
the process chamber; first and second electrodes arranged a
predetermined distance apart from each other and to face each other
within the process chamber, said target object being supported by
said second electrode to face said first electrode; first high
frequency apply means for applying a high frequency power having a
frequency of 50 MHz or higher to the first electrode so as to
generate a plasma of said etching gas between the first electrode
and the second electrode; and second high frequency apply means for
applying a high frequency power to the second electrode; said
second high frequency apply means also applying a high frequency
power to the first electrode so as to increase the thickness of the
plasma sheath formed on the first electrode.
2. The plasma etching apparatus according to claim 1, wherein said
first high frequency apply means applies a high frequency power of
50 to 200 MHz to said first electrode, and said second high
frequency apply means applies a high frequency power of 800 kHz to
28 MHz to said second electrode.
3. A plasma etching apparatus, comprising: a process chamber in
which a target object to be etched is housed; first and second
electrodes arranged a predetermined distance apart from each other
and in a manner to face each other within said process chamber;
first high frequency apply means for applying a first high
frequency power having a frequency of 50 MHz or higher to said
first electrode; second high frequency apply means for applying
second and third high frequency powers to the first electrode and
the second electrode, respectively, said second and third high
frequency powers having a frequency not lower than 2 MHz and not
higher than that of the first high frequency power, the frequency
of the second high frequency power being equal to that of the third
high frequency power, and the second high frequency power having a
reverse phase relative to the third high frequency power; exhaust
means for maintaining a predetermined reduced pressure within the
process chamber; and gas introducing means for introducing an
etching gas into the process chamber; wherein a plasma of the
etching gas is formed by allowing said high frequency powers to
form a high frequency electric field between the first and second
electrodes with the target object supported on the second
electrode, thereby performing an etching treatment of the target
object by the plasma, and the thickness of the plasma sheath formed
on the first electrode is increased by the second high frequency
power applied from the second high frequency apply means to the
first electrode.
4. The plasma etching apparatus according to claim 3, wherein said
second high frequency apply means comprises a high frequency power
source generating a high frequency power having a frequency not
lower than 2 MHz and lower than the frequency of the high frequency
power generated by said first high frequency apply means and a
transformer for distributing the power of said high frequency power
source to the first and second electrodes.
5. A plasma etching apparatus, comprising: a process chamber in
which a target object to be etched is housed; first and second
electrodes arranged a predetermined distance apart from each other
in a manner to face each other within said process chamber; first
high frequency apply means for applying a first high frequency
power having a frequency not lower than 50 MHz to said first
electrode; second high frequency apply means for applying second
and third high frequency powers to the first electrode and the
second electrode respectively, said high frequency powers having a
frequency not lower than 2 MHz and not higher than that of the
first high frequency power, the frequency of the second high
frequency power being equal to that of the third high frequency
power, and the second high frequency power having a phase
difference of 180.+-.45.degree. relative to the third high
frequency power; exhaust means for maintaining a predetermined
reduced pressure within the process chamber; and gas introducing
means for introducing an etching gas into the process chamber;
wherein a plasma of the etching gas is formed by allowing said high
frequency powers to form a high frequency electric field between
the first and second electrodes with the target object supported on
the second electrode, thereby performing an etching treatment of
the target object by the plasma, and the thickness of the plasma
sheath formed on the first electrode is increased by the second
high frequency power applied from the second high frequency apply
means to the first electrode.
6. The plasma etching apparatus according to claim 5, wherein said
second high frequency apply means comprises a high frequency
oscillator generating a high frequency power having a frequency not
lower than 2 MHz and lower than the frequency of the first high
frequency power means, amplifying means for amplifying the high
frequency power generated from said high frequency oscillator so as
to apply the amplified high frequency power to the first and second
electrodes, and a phase shift means for shifting the phase of the
high frequency power applied to at least one of the first electrode
and the second electrode.
7. The plasma etching apparatus according to claim 5, wherein the
frequency of the second and third high frequency powers generated
from said second high frequency apply means falls within a range of
between 2 MHz and 27 MHz.
8. The plasma etching apparatus according to claim 5, wherein the
first frequency of the high frequency power generated from said
first high frequency apply means is about 60 MHz, and the frequency
of the second and third high frequency power generated from said
second high frequency apply means is about 2 MHz.
9. The plasma etching apparatus according to claim 5, wherein said
second high frequency apply means applies the second and third high
frequency powers to said first electrode and said second electrode
at a ratio falling within a range of between 6:4 and 4:6.
10. A plasma etching apparatus, comprising: a process chamber in
which a target object to be processed is housed; exhaust means for
maintaining a desired reduced pressure state within the process
chamber; a gas introducing means for introducing an etching gas
into the process chamber; first and second electrodes arranged a
predetermined distance apart from each other to face each other
within the process chamber, said target object being supported on
said second electrode to face said first electrode; first high
frequency apply means for applying a first high frequency power to
the first electrode so as to cause said etching gas to form a
plasma between the first electrode and the second electrode; second
high frequency apply means for applying a second high frequency
power having a frequency lower than that of the first high
frequency power to the second electrode; third high frequency apply
means for superposing a third high frequency power having a
frequency lower than that of the first high frequency power and
higher than that of the second high frequency power on the first
high frequency power; and phase control means for adjusting the
phase difference between the second high frequency power and the
third high frequency power.
11. The plasma etching apparatus according to claim 10, wherein the
frequency of said third high frequency power is set equal to that
of said second high frequency power.
12. The plasma etching apparatus according to claim 10, wherein
said first high frequency apply means comprises a first high
frequency power source, a first matching device connected between
said first high frequency power source and said first electrode,
and a capacitor connected between said first matching device and
the first electrode with a wiring interposed therebetween, and
wherein said second high frequency apply means comprises a second
high frequency power source, and a second matching device connected
between said second high frequency power source and said second
electrode, and wherein said third high frequency apply means
comprises a third high frequency power source, a third matching
device connected between said third high frequency power source and
said wiring, and a band pass filter connected between said third
matching device and said wiring.
13. The plasma etching apparatus according to claim 12, wherein
said phase control means comprises a phase controller having an
input side connected to said second and third matching devices and
having an output side connected to said second and third high
frequency power sources, said phase controller serving to control
the phase of the high frequency power generated from at least one
of the second and third high frequency power sources so as to
adjust the phase difference between the high frequency powers
generated from the second and third high frequency power sources in
a manner to form a uniform plasma.
14. A plasma etching method, comprising the steps of: disposing a
target object to be processed on a second electrode in a manner to
face a first electrode with a predetermined space provided
therebetween, said first and second electrodes being arranged
within a process chamber having a reduced pressure; introducing an
etching gas into said process chamber; applying a high frequency
power having a frequency not lower than 50 MHz from a first high
frequency apply means to the first electrode to cause said etching
gas to generate a plasma between the first electrode and the second
electrode; and applying a high frequency power from a second high
frequency apply means to the second electrode; said second high
frequency apply means also applying a high frequency power to the
first electrode so as to increase the thickness of the plasma
sheath formed on the first electrode.
15. The plasma etching method according to claim 14, wherein said
first high frequency apply means applies a high frequency power of
50 to 200 MHz to said first electrode, and said second high
frequency apply means applies a high frequency power of 800 kHz to
28 MHz to said second electrode.
16. A plasma etching method, comprising the steps of: disposing a
target object to be processed on a second electrode in a manner to
face a first electrode with a predetermined space provided
therebetween, said first and second electrodes being arranged
within a process chamber having a reduced pressure; introducing an
etching gas into said process chamber; applying a first high
frequency power to the first electrode to cause said etching gas to
generate a plasma between the first electrode and the second
electrode; applying a high frequency power having a frequency lower
than that of said first high frequency power to the second
electrode; adjusting the phase of the frequency of at least one of
the first high frequency power and the second high frequency power
so as to provide a predetermined phase difference between the first
and second high frequency powers; and applying a third high
frequency power to the first electrode such that the third high
frequency power is superposed on the first high frequency power.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation-in-Part of Application No.
PCT/JP99/06619, filed Nov. 26, 1999.
[0002] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Applications No. 10-336886,
filed Nov. 27, 1998; and No. 11-308765, filed Oct. 29, 1999, the
entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to a plasma etching apparatus
and method for applying a plasma processing to a substrate such as
a semiconductor wafer.
[0004] In the manufacturing process of a semiconductor device,
widely employed is a plasma etching treatment in which a plasma
etching is applied to a target object or a semiconductor wafer
(including a semiconductor wafer itself and a semiconductor wafer
having a single film or a plurality of films formed thereon).
Various types of plasma etching apparatuses are employed for the
plasma etching treatment. Particularly, a capacitance coupling type
parallel plate plasma processing apparatus is mainly used as the
plasma etching apparatus.
[0005] In the capacitance coupling type parallel plate plasma
etching apparatus, a pair of parallel plate electrodes (upper and
lower electrodes) are arranged within a chamber a predetermined
distance apart from each other to face each other. An etching gas
is introduced into the chamber and, at the same time, a high
frequency power is applied to one of the electrodes to form a high
frequency electric field between the two electrodes. A plasma of
the etching gas is formed by the high frequency electric field so
as to apply a plasma etching to the semiconductor wafer.
[0006] Where a film formed on the semiconductor wafer, e.g., an
oxide film, is etched by using the capacitance coupling type
parallel plate plasma etching apparatus of the construction
described above, a plasma of an intermediate density is formed by
setting up an intermediate pressure within the chamber so as to
make it possible to perform the optimum radical control. As a
result, a suitable plasma state can be obtained so as to achieve an
etching with a high selectivity ratio, with a high stability and
with a high reproducibility.
[0007] To be more specific, it is described in "1997 DRY PROCESS
SYMPOSIUM P385-390" that a high frequency of 27.12 MHz for plasma
formation is applied to the upper electrode so as to form a plasma,
and a high frequency of 800 kHz is applied to the lower electrode
so as to draw the ions generated by the plasma onto the lower
electrode, making it possible to perform a satisfactory etching
under the pressure of 20 to 100 mTorr.
[0008] However, miniaturization of the design rule in USLI further
proceeds in recent years, leading to demands for a higher aspect
ratio in the shape of the hole. Under the conventional conditions,
it is difficult to meet the requirement sufficiently.
[0009] The conventional plasma etching, in which a semiconductor
wafer is disposed on the lower electrode, will now be described
with reference to FIG. 8. A reference numeral 111 shown in the
figure represents a resist layer acting as a mask for the selective
etching. Reference numerals 112, 114 and 117 represent insulating
films (SiO.sub.2 films), respectively. Further, reference numerals
113 and 115 represent an aluminum wiring and a gate wiring,
respectively.
[0010] As shown in the figure, that portion of the resist layer 111
which is in the vicinity of a plasma sheath S is charged negative
in the etching step, with the result that the electrons supplied
from a plasma P are mainly moved in the lateral direction,
resulting in failure to enter a contact hole 101 having a large
aspect ratio. On the other hand, cations are accelerated by the
plasma sheath so as to reach the bottom of the contact hole. As a
result, the bottom portion (exposed portion of the aluminum wiring)
103 of the contact hole 101 is charged positive. On the other hand,
both electrons and cations are accelerated to arrive at the space
portion (exposed portion of the semiconductor wafer) 105 in which
the contact hole is not formed without difficulty. As a result, a
strong electric field is applied to the thin insulating film 117
positioned below the gate electrode 116 so as to bring about an
insulation breakdown called shading damage.
DISCLOSURE OF INVENTION
[0011] An object of the present invention is to provide a plasma
etching apparatus and method, which permit obtaining a suitable
plasma state, which is capable of coping with the miniaturization
of the etching pattern, and which does not bring about a shading
damage.
[0012] As a result of an extensive research on a plasma etching
capable of coping with the required miniaturization, the present
inventors have found that a plasma can be formed with a lower
pressure condition by increasing the frequency of the high
frequency power applied to the upper electrode and the lower
electrode, e.g., by applying a high frequency power of 60 MHz to
the upper electrode and a high frequency power of 2 MHz to the
lower electrode, making it possible to form a plasma of a higher
density while maintaining a radical dissociation controllability
substantially equal to that of the conventional capacitance
coupling type parallel plate plasma processing apparatus and, to
cope with the further miniaturization.
[0013] However, it has also been found that, if the frequency of
the high frequency power applied to the upper electrode is
increased, a new problem is generated that the etching uniformity
is rendered poor. To be more specific, as shown by a broken line in
FIG. 1A, the plasma sheath on the side of an upper electrode is
rendered very thin in the central portion of the electrode, and the
plasma sheath of a lower electrode is rendered thick in the central
portion of the electrode. It follows that the plasma is rendered
nonuniform in a direction parallel to the electrodes.
[0014] The difficulty is caused by the phenomenon that higher
harmonic waves, which are absolutely generated when a high
frequency power is applied, form a standing wave within the plane
of the upper electrode. Since the standing wave has a large
amplitude in the center of the upper electrode, the standing wave
contributes to the plasma generated in the vicinity of the upper
electrode, with the result that the sheath in the central portion
of the upper electrode is rendered thinner than in the edge
portions (peripheral portion). However, where the frequency of the
power applied to the upper electrode is relatively low as in the
conventional apparatus, e.g., where the frequency is lower than 50
MHz, the plasma density is not high and, thus, the plasma sheath is
thick. It follows that the uniformity of the plasma is not greatly
affected by the standing wave. Also, where the frequency is lower
than 50 MHz, the wavelength of the higher harmonic wave is large
compared with the diameter of the upper electrode, with the result
that the influence given by the standing wave is diminished.
[0015] If the frequency of the high frequency power applied to the
upper electrode is increased so as to increase the plasma density,
the plasma sheath is rendered thin as a whole. Therefore, if the
plasma sheath in the central portion of the upper electrode is
affected by the standing wave, the plasma sheath is made markedly
thin in the central portion of the electrode in the extreme case,
as shown in the figure, leading to a poor uniformity of plasma.
[0016] On the other hand, it should be noted in conjunction with
the plasma sheath of the lower electrode that, since the plasma
sheath is thin in the central portion of the upper electrode, the
capacitance in that portion is increased. As a result, an electric
current flows in a concentrated fashion into the filter of 2 MHz so
as to increase the thickness of the plasma sheath. It follows that
the ions in the plasma in the central portion are further
accelerated so as to make the etching rate in the central portion
of the wafer higher than that in the peripheral portion of the
wafer. As a result, the uniformity of the etching is lowered.
[0017] As a result of the continued research conducted in an
attempt to overcome the new defect described above, the present
inventors have found that it is possible to increase the thickness
of the plasma sheath by applying a specified high frequency power
in addition to the high frequency power described above to the
upper and lower electrodes so as to diminish the fluctuation in the
thickness of the plasma sheath. It has also been found that, in
order to increase the thickness of the plasma sheath so as to
diminish the fluctuation in the thickness of the plasma sheath, it
is necessary to apply a high frequency power of a specified
frequency to each of the upper and lower electrodes, the frequency
of the high frequency power applied to the both electrodes being
the same, in substantially the reverse phase or in the phase in the
vicinity of the reverse phase.
[0018] It has also been found that, if a high frequency power of a
specified frequency is applied to each of the upper and lower
electrodes, the frequency of the high frequency power applied to
the both electrodes being the same, in substantially the reverse
phase or in the phase in the vicinity of the reverse phase, the
shading damage is unlikely to take place.
[0019] According to a first aspect of the present invention, which
has been achieved on the basis of the finding described above,
there is provided a plasma etching apparatus, comprising:
[0020] a process chamber in which a target object to be processed
is housed;
[0021] exhaust means for maintaining a predetermined reduced
pressure within the process chamber;
[0022] gas introducing means for introducing an etching gas into
the process chamber;
[0023] first and second electrodes arranged a predetermined
distance apart from each other and to face each other within the
process chamber, the target object being supported by the second
electrode to face the first electrode;
[0024] first high frequency apply means for applying a high
frequency power having a frequency of 50 MHz or higher to the first
electrode so as to generate a plasma of the etching gas between the
first electrode and the second electrode; and
[0025] second high frequency apply means for applying a high
frequency power to the second electrode;
[0026] the second high frequency apply means also applying a high
frequency power to the first electrode so as to increase the
thickness of the plasma sheath formed on the first electrode.
[0027] According to a second aspect of the present invention, there
is provided a plasma etching apparatus, comprising:
[0028] a process chamber in which a target object to be etched is
housed;
[0029] first and second electrodes arranged a predetermined
distance apart from each other and in a manner to face each other
within the process chamber;
[0030] first high frequency apply means for applying a first high
frequency power having a frequency of 50 MHz or higher to the first
electrode;
[0031] second high frequency apply means for applying a second and
third high frequency powers to the first electrode and the second
electrode respectively, the second and third high frequency powers
having a frequency not lower than 2 MHz and not higher than that of
the first high frequency power, the frequency of the second high
frequency power being equal to that of the third high frequency
power, and the second high frequency power having a reverse phase
relative to the third high frequency power;
[0032] exhaust means for maintaining a predetermined reduced
pressure within the process chamber; and
[0033] gas introducing means for introducing an etching gas into
the process chamber;
[0034] wherein a plasma of the etching gas is formed by allowing
the high frequency powers to form a high frequency electric field
between the first and second electrodes with the target object
supported on the second electrode, thereby performing an etching
treatment of the target object by the plasma, and
[0035] the thickness of the plasma sheath formed on the first
electrode is increased by the second high frequency power applied
from the second high frequency apply means to the first
electrode.
[0036] According to a third aspect of the present invention, there
is provided a plasma etching apparatus, comprising:
[0037] a process chamber in which a target object to be processed
is housed;
[0038] first and second electrodes arranged a predetermined
distance apart from each other in a manner to face each other
within the process chamber;
[0039] first high frequency apply means for applying a first high
frequency power having a frequency not lower than 50 MHz to the
first electrode;
[0040] second high frequency apply means for applying second and
third high frequency powers to the first electrode and the second
electrode respectively, the second and third high frequency powers
having a frequency not lower than 2 MHz and not higher than that of
the first high frequency power, the frequency of the second high
frequency power being equal to that of the third high frequency
power, and the second high frequency power having a phase
difference of 180.+-.45.degree. relative to the third high
frequency power;
[0041] exhaust means for maintaining a predetermined reduced
pressure within the process chamber; and
[0042] gas introducing means for introducing an etching gas into
the process chamber;
[0043] wherein a plasma of the etching gas is formed by allowing
the high frequency powers to form a high frequency electric field
between the first and second electrodes with the target object
supported on the second electrode, thereby performing an etching
treatment of the target object by the plasma, and
[0044] the thickness of the plasma sheath formed on the first
electrode is increased by the second high frequency power applied
from the second high frequency apply means to the first
electrode.
[0045] The plasma etching apparatus of the present invention
comprises first high frequency apply means for applying a high
frequency power having a frequency not lower than 50 MHz to the
first electrode and second high frequency apply means for applying
a high frequency power not only to the second electrode but also to
the first electrode for increasing the thickness of the plasma
sheath formed on the first electrode, with the result that, even if
the plasma sheath is affected by the standing wave, the ratio in
the change of the thickness of the plasma sheath is made relatively
small so as to make the plasma more uniform. To be more specific,
the second high frequency apply means applies second and third high
frequency powers having a frequency not lower than 2 MHz and lower
than the frequency of the first high frequency power to the first
electrode and the second electrode, the frequency of the second
high frequency power being equal to that of the third high
frequency power, and the second high frequency power having a
reverse phase relative to the third high frequency power. Thus, the
second high frequency power having a relatively low frequency is
applied from the second high frequency apply means to the first
electrode in addition to the first high frequency power applied
from the first high frequency apply means to the first electrode.
It follows that, as shown in FIG. 1B, a plasma sheath corresponding
to the low frequency, e.g., 2 MHz, of the second high frequency
apply means is superposed on the plasma sheath of the frequency,
e.g., 60 MHz, of the first high frequency apply means so as to form
a thick plasma sheath on the first electrode. Also, the plasma
sheath corresponding to 2 MHz is thicker than the plasma sheath
corresponding to 60 MHz. It follows that, even if the plasma sheath
is affected by the standing wave, the ratio in the change of the
thickness of the plasma sheath is small so as to diminish the
degree of reduction in the uniformity of the plasma. Also, since
the thickness of the plasma sheath of the first electrode is
increased, the change in the capacitance caused by the standing
wave is small so as to make uniform the current flowing into the
second electrode. As a result, the plasma sheath of the second
electrode is made substantially uniform, as shown in the figure. It
follows that, in the present invention, it is possible to cope with
the miniaturization by a high density plasma and to ensure
uniformity of the etching by a uniform plasma. Incidentally, FIG.
1B shows the state that high frequency powers of reverse phases
having a frequency of 2 MHz are applied to the upper electrode
(first electrode) and the lower electrode (second electrode) by
using a power splitter used in the second high frequency apply
means.
[0046] It should also be noted that, since the second and third
high frequency powers applied from the second high frequency apply
means to the first and second electrodes are substantially in
reverse phases, the intensity of the electric field in the sheath
portion is kept at a value higher than a predetermined value so as
to make it possible to increase the space potential of plasma. In
addition, the ionization rate is increased so as to increase the
plasma density. As a result, the ions and electrons are allowed to
have a high energy. Also, the ionization rate is increased in the
vicinity of the electrode so as to increase the high speed electron
flux. It follows that the electrons in the plasma are allowed to
reach easily the bottom portion of the contact hole so as to
neutralize the positive charge within the hole and, thus, to
suppress the shading damage.
[0047] In the present invention, the prominent effects described
above can be produced by applying second and third high frequency
powers substantially forming reverse phases to the first and second
electrodes. However, these high frequency powers need not form
reverse phases for producing these effects as far as the phase
difference is close to the reverse phase. To be more specific,
desired effects can be obtained if the phase difference between the
second and third high frequency powers falls within a range of
180.+-.45.degree..
[0048] In the present invention, the first high frequency apply
means applies a high frequency power having a frequency not lower
than 50 MHz. If the frequency is lower than 50 MHz, it is difficult
to obtain a desired high density plasma, resulting in failure to
cope with the required miniaturization. Also, if the frequency is
lower than 50 MHz, the problem itself to be solved by the present
invention does not take place.
[0049] In the second aspect of the present invention, it is
possible for the second high frequency apply means to comprise a
high frequency power source having a frequency not lower than 2 MHz
and lower than that of the first high frequency apply means and a
transformer for distributing the power of the high frequency power
source to the first and second electrodes.
[0050] In the second and third aspects of the present invention,
the frequency of the second and third high frequency powers is not
lower than 2 MHz. If the frequency is not lower than 2 MHz, the
ions are unlikely to follow the high frequency power application,
with the result that it is possible to suppress the damage done to
the target object when the ions are drawn to the target object.
[0051] In each of the second aspect and the third aspect of the
present invention, it is possible for the second high frequency
apply means to comprise a high frequency oscillator having a
frequency not lower than 2 MHz and lower than the frequency of the
first high frequency apply means, amplifying means for amplifying
the high frequency so as to apply a predetermined high frequency
power to each of the first electrode and the second electrode, and
a phase shift means for shifting the phase of the high frequency
applied to the first electrode or the second electrode.
[0052] Also, in each of the second aspect and the third aspect of
the present invention, it is desirable for the frequency of the
second and third high frequency powers to fall within a range of
between 2 MHz and 27 MHz. For example, it is desirable for the
frequency of the first high frequency power to be about 60 MHz and
for the frequency of the second and third high frequency powers to
be about 2 MHz. Further, it is desirable for the ratio of the power
supplied from the second high frequency apply means to the first
electrode to the power supplied from the second high frequency
apply means to the second electrode to fall within a range of
between 6:4 and 4:6.
[0053] According to a fourth aspect of the present invention, there
is provided a plasma etching apparatus, comprising:
[0054] a process chamber in which a target object to be etched is
housed;
[0055] exhaust means for maintaining a desired reduced pressure
state within the process chamber;
[0056] a gas introducing means for introducing an etching gas into
the process chamber;
[0057] first and second electrodes arranged a predetermined
distance apart from each other to face each other within the
process chamber, the target object being supported on the second
electrode to face the first electrode;
[0058] first high frequency apply means for applying a first high
frequency power to the first electrode so as to cause the etching
gas to form a plasma between the first electrode and the second
electrode;
[0059] second high frequency apply means for applying a second high
frequency power having a frequency lower than that of the first
high frequency power to the second electrode;
[0060] third high frequency apply means for superposing a third
high frequency power having a frequency lower than that of the
first high frequency power and higher than that of the second high
frequency power on the first high frequency power; and
[0061] phase control means for adjusting the phase difference
between the second high frequency power and the third high
frequency power.
[0062] According to a fifth aspect of the present invention, there
is provided a plasma etching method, comprising the steps of:
[0063] disposing a target object to be processed on a second
electrode in a manner to face a first electrode with a
predetermined space provided therebetween, the first and second
electrodes being arranged within a process chamber having a reduced
pressure;
[0064] introducing an etching gas into the process chamber;
[0065] applying a high frequency power having a frequency not lower
than 50 MHz from a first high frequency apply means to the first
electrode to cause the etching gas to generate a plasma between the
first electrode and the second electrode; and
[0066] applying a high frequency power from a second high frequency
apply means to the second electrode;
[0067] the second high frequency apply means also applying a high
frequency power to the first electrode so as to increase the
thickness of the plasma sheath formed on the first electrode.
[0068] It may be apparent that the method according to the fifth
aspect of the present invention produces effects similar to those
produced by the invention according to the first aspect of the
present invention.
[0069] Further, according to a sixth aspect of the present
invention, there is provided a plasma etching method, comprising
the steps of:
[0070] disposing a target object to be processed on a second
electrode in a manner to face a first electrode with a
predetermined space provided therebetween, the first and second
electrodes being arranged within a process chamber having a reduced
pressure;
[0071] introducing an etching gas into the process chamber;
[0072] applying a first high frequency power to the first electrode
to cause the etching gas to generate a plasma between the first
electrode and the second electrode;
[0073] applying a high frequency power having a frequency lower
than that of the first high frequency power to the second
electrode;
[0074] adjusting the phase of the frequency of at least one of the
first high frequency power and the second high frequency power so
as to provide a predetermined phase difference between the first
and second high frequency powers; and
[0075] applying a third high frequency power to the second
electrode such that the third high frequency power is superposed on
the first high frequency power.
[0076] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0077] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0078] FIG. 1A is a view for explaining the principle of the prior
art;
[0079] FIG. 1B is a view for explaining the principle of the
present invention;
[0080] FIG. 2 is a cross sectional view schematically showing an
etching apparatus according to a first embodiment of the present
invention;
[0081] FIG. 3 is a view showing the result of simulation in respect
of the potential distribution of plasma;
[0082] FIG. 4 is a graph showing the space potential of plasma;
[0083] FIGS. 5A and 5B are graphs showing the ionization rates of
the plasma in the vicinity of the electrode and the bulk;
[0084] FIG. 6 is a view showing another example of a second high
frequency power apply mechanism;
[0085] FIG. 7 is a view for schematically showing an etching
apparatus according to a second embodiment of the present
invention; and
[0086] FIG. 8 is a view showing the concept of a shading damage in
the conventional apparatus.
DETAILED DESCRIPTION OF THE INVENTION
[0087] A first embodiment of the present invention will now be
described with reference to the accompanying drawings.
[0088] Specifically, FIG. 2 is a cross sectional view schematically
showing an etching apparatus 1 according to the first embodiment of
the present invention. The etching apparatus 1 is constructed as a
capacitance coupling type parallel plate etching apparatus in which
upper and lower electrode are arranged in parallel and a power
source for plasma formation is connected to one of these upper and
lower electrodes.
[0089] To be more specific, the etching apparatus 1 comprises a
cylindrical chamber 2 made of aluminum and having, for example, an
anodized aluminum treatment (anodic oxidation treatment) applied to
the inner surface. The chamber 2 is connected to the ground for
safety. A substantially columnar susceptor table 4 for supporting a
target object to be processed, e.g., a semiconductor wafer
(hereinafter referred to as a wafer) W, is arranged in the bottom
portion of the chamber 2 with an insulating plate 3 made of, for
example, a ceramic material, interposed therebetween. A susceptor 5
constituting a lower electrode (plate like electrode) is arranged
on the susceptor table 4. The susceptor 5 is connected to the
ground through a high pass filter (HPF) 6.
[0090] A cooling chamber 7 is formed within the susceptor table 4.
A coolant such as a liquid nitrogen is introduced into the cooling
chamber 7 through a coolant introducing pipe 8 and discharged from
within the cooling chamber 7 through a coolant discharge pipe 9, so
as to be circulated within the cooling chamber 7. During
circulation of the coolant within the coolant chamber 7, the wafer
W disposed on the susceptor 5 is cooled by the coolant via the
susceptor table 4 and the susceptor 5 arranged on the susceptor
table 4 so as to control the process surface of the wafer W at a
desired temperature.
[0091] The susceptor 5 is in the shape of a disc, and an
electrostatic chuck 11 substantially equal in shape to the wafer W
is formed on the disc-like susceptor 5. The electrostatic chuck 11
is constructed such that an electrode 12 is interposed between
insulating materials. A DC voltage of, for example, 1.5 kV is
applied from a DC power source 13 to the electrode 12, with the
result that the wafer W is electrostatically sucked on the
electrostatic chuck by the Coulomb force or the Johnson-Rahbeck
force.
[0092] A gas passageway 14 for supplying a heat transfer medium,
e.g., a He gas, to the back surface of the wafer w is formed to
extend through the insulating plate 3, the susceptor table 4, the
susceptor 5 and the electrostatic chuck 11. The low temperature of
the susceptor 5 is effectively transferred by the heat transfer
medium to the wafer W so as to maintain the wafer W at a
predetermined temperature.
[0093] An annular focus ring 15 is arranged on the upper peripheral
portion of the susceptor 5 in a manner to surround the wafer W. The
annular focus ring 15, which is made of a conductive material such
as silicon, serves to improve the uniformity of the etching.
[0094] An upper electrode (plate like electrode) 21 is arranged
above the lower electrode 5 in parallel to the susceptor 5 and in a
manner to face the lower electrode 5 with a predetermined clearance
provided therebetween. The upper electrode 21 is supported in an
upper portion of the chamber 2 with an insulating material 22
interposed therebetween so as to constitute a surface facing the
susceptor 5, and includes an electrode plate 24 having a large
number of spurting holes 23 and an electrode support member 25
supporting the electrode plate 24. The electrode plate 24 is formed
of, for example, silicon or an amorphous carbon. On the other hand,
the electrode support member 25 is made of a conductive material
such as an aluminum plate having the surface subjected to an
anodized aluminum treatment. Incidentally, the lower electrode 5
and the upper electrode 21 are positioned about 10 to 60 mm apart
from each other.
[0095] A gas introducing port 26 is formed in the center of the
electrode support member 25 of the upper electrode 21. A gas supply
pipe 27 is connected to the gas introducing port 26, and an etching
gas supply source 30 is connected to the gas supply pipe 27 via a
valve 28 and a mass flow controller 29. A process gas or etching
gas for the etching treatment is supplied from the etching gas
supply source 30. The process gas supplied from the etching gas
supply source 30 includes, for example, a CF.sub.4 gas.
[0096] A discharge pipe 31 is connected to the bottom portion of
the chamber 2. An exhaust apparatus 35 is connected to the exhaust
pipe 31. The exhaust apparatus 35 is equipped with a vacuum pump
such as a turbo molecular pump so as to evacuate the chamber 2 to a
reduced pressure of, for example about 1 mTorr (0.133 Pa). Also, a
gate valve 32 is mounted to the side wall of the chamber 2. The
wafer W is transferred between the chamber 2 and an adjacent load
lock chamber (not shown) with the gate valve 32 kept open.
[0097] The mechanism of forming a plasma will now be described.
[0098] The apparatus of the first embodiment shown in FIG. 2
comprises a first high frequency apply mechanism 100 for applying a
high frequency power having a relatively high frequency to the
upper electrode 21 and a second high frequency apply mechanism 200
for applying high frequency powers having relatively low
frequencies of substantially reverse phases to the susceptor 5
acting as the lower electrode and to the upper electrode 21. The
second high frequency apply mechanism 200 is constructed to apply
high frequency powers of the same frequency to the susceptor 5 and
to the upper electrode 21.
[0099] The first high frequency apply mechanism 100 comprises a
first high frequency power source 50, which is connected to the
upper electrode 21 via a matching device 51 and a high pass filter
(HPF) 52. The first high frequency power source 50 has a frequency
not lower than 50 MHz, preferably between 60 MHz and 200 MHz. A
high density plasma is formed within the chamber 2 under a low
pressure condition by applying a high frequency power having such a
high frequency to the upper electrode 21. It is more desirable for
the first high frequency power source 50 to have a frequency of 60
MHz and an output power of 2,000W.
[0100] The second high frequency power source 200 comprises a
second high frequency power source 40, which is connected to the
primary side of a transformer 42 constituting a power splitter via
a matching device 41. A ground terminal 43 is connected to the
secondary side of the transformer 42. The secondary side of the
transformer 42 is connected to the lower electrode 5 via a low pass
filter (LPF) 45 and is also connected to the upper electrode 21 via
a low pass filter (LPF) 44. It follows that the power of the high
frequency power source 40 can be distributed with an optional ratio
by selecting the opposition of the ground terminal 43. For example,
where the output power of the high frequency power source 40 is
1,000W, it is possible to distribute 600W to the lower electrode 5
and 400W to the upper electrode 21. Also, high frequency powers
substantially forming reverse phases, i.e., differing from each
other in phase by 180.degree., are applied to the lower and upper
electrodes 5, 21. The second high frequency power source 40 has a
frequency lower than that of the first high frequency power source
50. Specifically, the second high frequency power source 40 has a
frequency of, preferably 800 kHz to 28 MHz, more preferably 2 MHz
to 13.56 MHz. If the second high frequency power source 40 has a
frequency exemplified above, it is possible to suppress the damage
done to the wafer W by the ions drawn to the lower electrode 5. It
is substantially desirable for the second high frequency power
source 40 to have a frequency of 2 MHz. As described herein later,
it has been experimentally confirmed that, in order to effectively
prevent the shading damage, it is desirable for the distribution
ratio between the upper electrode 21 and the lower electrode 5 to
fall within a range of between 4:6 and 6:4.
[0101] Where a silicon oxide film (SiO.sub.2 film) formed on a
silicon wafer (target object) W is etched by the etching apparatus
1 of the construction described above, the gate valve 32 is opened
first and, then, the wafer W is introduced from a load lock chamber
(not shown) into the chamber 2 so as to be disposed on the
electrostatic chuck 11. Then, a DC voltage is applied from the high
DC power source 13 so as to permit the wafer W to be
electrostatically sucked on the electrostatic chuck 11. Then, the
gate valve 32 is closed, and the pressure within the chamber 2 is
reduced by the exhaust mechanism 35 to a predetermined degree of
vacuum.
[0102] In the next step, the valve 28 is opened so as to permit,
for example, a CF.sub.4 gas to be supplied from the etching gas
supply source 30 to the hollow portion of the upper electrode 21
through the process gas supply pipe 27 and the gas introducing port
26 while the flow rate of the CF.sub.4 gas is being controlled by
the mass flow controller 29. Further, the CF.sub.4 passes through
the spurting ports 23 of the electrode plate 24 so as to be
discharged uniformly toward the wafer W, as denoted by arrows in
FIG. 2.
[0103] In the state that the pressure within the chamber 2 is
maintained at, for example, 20 mTorr (2.66 Pa), a high frequency
of, for example, 60 MHz is applied from the high frequency power
source 50 of in the first high frequency apply mechanism 100 to the
upper electrode 21. As a result, a high frequency electric field is
formed between the upper electrode 21 and the lower electrode 5 so
as to dissociate the process gas to form a plasma. On the other
hand, high frequency powers of 2 MHz in substantially reverse
phases (differing from each other in phase by 180.degree.) are
supplied from the high frequency power source 40 included in the
second high frequency apply mechanism 200 to the susceptor 5 and to
the upper electrode 21 through the transformer 42.
[0104] The component applied from the second high frequency apply
mechanism 200 to the upper electrode 21 performs the function of
increasing the thickness of the plasma sheath formed on the side of
the upper electrode 21 by the high frequency of, for example, 60
MHz supplied from the first high frequency apply mechanism 100 to
the upper electrode. As a result, the nonuniformity in the
thickness of the plasma sheath formed on the surface of the upper
electrode 21 by the higher harmonic wave forming the standing wave
is moderated so as to form a uniform plasma.
[0105] On the other hand, the component applied from the second
high frequency apply mechanism 200 to the lower electrode susceptor
5 performs the function of positively drawing mainly the ions in
the gaseous molecules converted into a plasma toward the susceptor
5. By this ion assist, an etching having a higher anisotropy can be
applied to the oxide film of the wafer W mounted on the susceptor
5. In this case, since the frequency is not lower than 2 MHz, a
damage is unlikely to be done to the wafer W.
[0106] As described above, a high density plasma can be formed
under a low pressure by applying a high frequency power having a
relatively high frequency not lower than 50 MHz, e.g., 60 MHz. In
addition, since the etching selectivity and anisotropy can be
enhanced by applying a high frequency power having a lower
frequency, e.g., 2 MHz, to the lower electrode 5, it is possible to
apply a fine processing to the wafer W. Further, since it is
possible to eliminate the nonuniformity of plasma that takes place
in the case of applying a high frequency power having a relatively
high frequency, e.g., 60 MHz, to the upper electrode 21, it is
possible to ensure the uniformity of the plasma processing.
[0107] As described previously, high frequency powers of 2 MHz in
substantially reverse phases are applied from the second high
frequency apply mechanism 200 to both the lower and upper
electrodes 5, 21 so as to diminish the fluctuation in the sheath
thickness. As a result, the intensity of the electric field in the
sheath portion bears a value higher than a predetermined value so
as to increase the space potential of the plasma. It follows that
the ionization rate is increased so as to increase the plasma
density and, thus, the ions and the electrons are allowed to have a
high energy. It is also possible to increase the ionization rate in
the vicinity of the electrode so as to increase the high speed
electron flux. It follows that the electrons within the plasma are
allowed to reach easily the bottom portion of the contact hole so
as to neutralize the positive charge within the hole, thereby
suppressing the shading damage.
[0108] It should also be noted that, since the low pass filter
(LPF) 44 is interposed between the secondary side of the
transformer 42 and the upper electrode 21 and the low pass filter
(LPF) 45 is interposed between the secondary side of the
transformer 42 and the lower electrode 5, it is impossible for the
high frequency power of, for example, 60 MHz supplied from the
first high frequency source 50 to enter the routes including the
low pass filters (LPF) 44 and 45. Also, since the high pass filter
(HPF) 52 is included in the route of supplying the high frequency
power of the first high frequency power source 50, it is impossible
for the high frequency power having a low frequency of, for
example, 2 MHz supplied from the second high frequency power source
40 to enter the route of supplying the high frequency power of the
first high frequency power source 50. It follows that it is
possible to realize a stable process. Incidentally, in view of such
a blocking function, it is possible to use another blocking means
in place of the low pass filters (LPF) 44, 45 and the high pass
filter (HPF) 52.
[0109] The result of the simulation of the plasma formed by the
plasma processing apparatus of the present invention will now be
described.
[0110] FIG. 3 shows graphs showing the potential distribution
within the space above the center of the wafer, covering the cases
where a high frequency power of 60 MHz was applied to the upper
electrode and a high frequency power of 2 MHz was applied to both
the upper electrode and the lower electrode with a distribution
ratio of 4:6 as in the present invention, and where a high
frequency power of 60 MHz was applied to the upper electrode and a
high frequency power of 2 MHz was applied to the lower electrode
alone as in the comparison example. In each of the graphs shown in
FIG. 3, the distance in a direction perpendicular to the plane of
the electrode is plotted on the abscissa, and the time covering one
period of the high frequency power of 2 MHz is plotted on the
ordinate. As shown in the graphs, the sheath thickness is stable in
the present invention, compared with the comparison example. It is
seen that the intensity of the electric field, which is denoted by
the gradient of the potential in the sheath portion, has a value
higher than a certain value. It should also be noted that the
plasma potential for the present invention is higher than that for
the comparison example as shown in FIG. 4, and the fluctuation in
the plasma potential in the present invention is smaller than that
in the comparison example. Further, the ionization rate in the
present invention is higher than that in the comparison example in
each of the bulk (plasma itself) and in the vicinity of the
electrode, as shown in FIGS. 5A and 5B. In other words, the plasma
density for the present invention is higher than that for the
comparison example. It has also been confirmed by the simulation
that the ions and the electrons are allowed to have a higher energy
so as to increase the high speed electron flux. Further, the time
for electrons within the plasma sheath to be migrated to reach the
wafer was examined by means of simulation. It has been found that
the electron migrating time for the comparison example was 3.3 nsec
in contrast to 3.2 nsec for the present invention. In other words,
electrons are migrated in a higher speed in the present invention.
It follows that the number of electrons reaching the bottom portion
103 of the contact hole 101 shown in FIG. 8 is increased in the
present invention so as to moderate the positive charge in the
bottom portion 103 and, thus, to suppress the shading damage.
[0111] As described above, it has been confirmed that the thickness
of the plasma sheath is unlikely to be fluctuated in the present
invention so as to suppress the shading damage.
[0112] An accelerating experiment of the shading damage was
actually conducted. It has been found that the yield was 59% for
the comparison example in contrast to 98% for the present
invention. Also, it has been confirmed that the shading damage can
be prevented particularly effectively in the case where the
distribution ratio of the high frequency power to the upper
electrode and to the lower electrode falls within a range of
between 4:6 and 6:4. It has also been confirmed that, where the
distribution ratio of the high frequency power to the upper
electrode and to the lower electrode is set at 6:4, the etching
selectivity ratio was higher than that in the comparison example
and that in the case where the distribution ratio was set at 4:6.
It is considered reasonable to understand that, in the case of
increasing the power applied to the upper electrode, the radical
distribution is increased in the vicinity of the wafer so as to
lead to the high etching selectivity ratio noted above.
[0113] The present invention is not limited to the embodiment
described above, making it possible to modify the embodiment
described above in various fashions. For example, in the embodiment
described above, a so-called power splitter was used in the second
high frequency apply mechanism 200. However, the second high
frequency apply mechanism 200 does not include to a power splitter,
as far as high frequency powers of reverse phases can be applied to
the upper and lower electrodes. For example, it is possible to
employ the circuit shown in FIG. 6. Specifically, a high frequency
oscillator 60 oscillating a high frequency power of, for example, 2
MHz is connected to the upper electrode 21 through an amplifier 61,
a matching device 62 and the low pass filter (LPF) 44 and is also
connected to the susceptor or lower electrode 5 through a phase
shift circuit 63, an amplifier 64, a matching device 65 and the low
pass filter (LPF) 45. The phase of the high frequency power applied
to the susceptor 5 is shifted by 180.degree. by the phase shift
circuit 63 so as to form a reverse phase. If the frequency is
increased, the transformer fails to perform its function.
Therefore, the construction shown in FIG. 6 is particularly
effective under a high frequency.
[0114] In the embodiment described above, high frequency powers
having reverse phases are applied to the upper electrode and the
lower electrode. However, it is not absolutely necessary for the
high frequency powers to have reverse phases, as far as the phases
of these high frequency powers are close to the reverse phases. To
be more specific, a desired effect can be obtained if the phase
shift falls within the range of 180.+-.45.degree.. The particular
construction can be achieved by adjusting the shift amount of the
phase shift circuit 63 shown in FIG. 6.
[0115] A plasma etching apparatus 140 according to the second
embodiment of the present invention will now be described with
reference to FIG. 7.
[0116] Specifically, the plasma etching apparatus 140 comprises a
conductive and hermetic process vessel 104 connected to the ground.
A process chamber 102 is defined within the process vessel 104. An
upper electrode plate (first electrode) 106 and a lower electrode
plate (second electrode) 108 are arranged to face each other within
the process chamber 102. These first and second electrodes 106 and
108 are arranged a predetermined distance apart from each other.
The lower electrode plate 108 is fixed to the lower wall of the
process vessel with an insulator 108a interposed therebetween, and
performs the function of a susceptor on the upper surface of which
is disposed a target object to be processed, e.g., a semiconductor
wafer having an SiO.sub.2 film formed thereon. It is possible for
the second electrode 108 to be constructed as shown in FIG. 2. An
inlet port 104a connected to an etching gas source 110 is formed in
an upper portion of the circumferential wall of the process vessel
104. On the other hand, an outlet port 104b connected to a vacuum
pump 109 is formed in a lower portion of the circumferential wall
of the process vessel 104. As a result, during the etching
treatment, an etching gas is supplied into the process chamber 102
through the inlet port 104a and, at the same time, the process
chamber is exhausted by the vacuum pump 109 so as to maintain a
predetermined reduced pressure within the process chamber 102.
[0117] It is possible for the first electrode 106 and the inlet
port 104a to be constructed to form a shower head as shown in FIG.
2.
[0118] A first high frequency power source 144 is connected to the
upper electrode plate 106 via a low pass filter 146, a first
matching device 148, and a capacitor 120. As a result, a first high
frequency power of 5 kW having a predetermined frequency, e.g., 50
to 200 MHz, preferably about 60 MHz, is supplied to the upper
electrode plate 106. It should be noted that the capacitor 120
passes the first high frequency power and serves to prevent a third
high frequency power, which is to be described herein later, from
entering the first matching device 148.
[0119] A second high frequency power source 122 is connected to the
lower electrode plate 108 via a second matching device 124. As a
result, a second high frequency power of 5 kw having a
predetermined frequency, e.g., 800 kHz to 28 MHz, preferably about
2 MHz, is supplied to the lower electrode plate 108.
[0120] Further, a third high frequency power source 126 is
connected to the wiring between the upper electrode plate 106 and
the capacitor 120 via a third matching device 128 and a band pass
filter 130. Therefore, a third high frequency power having a
frequency lower than that of the first high frequency power and not
lower than that of the second high frequency power is applied to
the upper electrode plate 106 in a manner to. superpose on the
first high frequency power. In this preferred embodiment, the third
high frequency power 126 is set at 2 kW with a frequency of about 2
MHz. The band pass filter 130 passes the third high frequency power
(2 MHz) and, at the same time, serves to prevent the first high
frequency power (60 MHz) from entering the third matching device
128. It follows that the band pass filter 130 and the capacitor 120
serve to prevent the undesired high frequency power from entering
the first and third matching devices 148, 128, thereby preventing
malfunctions of the matching devices.
[0121] The output side of a phase controller 132 is connected to
each of the second high frequency power source 122 and the third
high frequency power source 126. The input side of the phase
controller 132 is connected to the second matching device 124 and
to the third matching device 128. As a result, the second and third
power sources 122, 126 are controlled on the basis of the phase of
the second high frequency power source and the phase of the third
high frequency power source detected by the matching devices 124
and 128, respectively, so as to permit the phase of the second high
frequency power source 122 and the phase of the third high
frequency power source 126 to have a predetermined phase
difference.
[0122] The etching treatment using the etching apparatus 140 of the
construction described above will now be described.
[0123] In the first step, the target object (wafer) W is disposed
on the lower electrode 108, followed by supplying an etching gas
into the process chamber 102. At the same time, the process chamber
102 is evacuated to a predetermined pressure, e.g., 20 mTorr, and
the reduced pressure is maintained. Under this condition, the first
high frequency power is applied from the first high frequency power
source 144 to the upper electrode plate 106 so as to generate a
plasma of the etching gas between the two electrode plates 106,
108. At substantially the same time, the second high frequency
power is applied from the second high frequency power source 122 to
the lower electrode plate 108. Also, the third high frequency power
is superposed on the first high frequency power by the third high
frequency power source 126 and applied to the upper electrode 106
by detecting the phases of the first and second high frequency
powers so as to provide a predetermined phase difference, thereby
making the plasma density uniform. Under this condition, the
etching of the target object proceeds.
[0124] A uniform etching treatment can be applied to the SiO.sub.2
film formed on the wafer W with a high etching rate by the plasma
of the uniform density thus generated. Also, since the plasma
conforms uniformly with the wafer W, it is possible to prevent a
damage done to the target object by the nonuniformity of the
plasma.
[0125] In the embodiment described above, a semiconductor wafer W
is used as the target object to be processed. However, it is also
possible to apply the etching treatment to other substrates such as
a glass plate for a liquid crystal display (LCD) device.
[0126] As described above, each of the etching apparatus according
to the first to third aspects and the fifth aspect of the present
invention comprises first high frequency apply means for applying a
high frequency power of 50 MHz or higher to the first electrode and
second high frequency apply means for applying a high frequency
power to the second electrode. It should be noted that the second
high frequency apply means also applies the high frequency power to
the first electrode in order to increase the thickness of the
plasma sheath formed on the first electrode. Therefore, even if the
plasma sheath is affected by the standing wave, the ratio in the
change in the thickness of the plasma sheath is rendered relatively
small so as to make the plasma more uniform. To be more specific,
since the etching apparatus of the present invention comprises the
first high frequency apply means for applying a high frequency
power of 50 MHz or higher to the first electrode and the second
high frequency apply means for applying a high frequency power
having a frequency not lower than 2 MHz and lower than the
frequency of the high frequency power applied by the first high
frequency apply means to each of the first electrode and the second
electrode, the frequency of the high frequency power applied by
said second high frequency apply means to the first electrode being
equal to that of the high frequency power applied by the second
high frequency apply means to the second electrode, and the high
frequency power applied by said second high frequency apply means
to the first electrode substantially forming a reverse phase
relative to the high frequency power applied by the second high
frequency apply means to the second electrode, a high frequency
power having a relatively low frequency is applied from the second
high frequency apply means to the first electrode as well as the
high frequency power applied from the first high frequency apply
means to the first electrode. It follows that, in the plasma sheath
of the upper electrode, the portion corresponding to the high
frequency power of the second high frequency apply means having a
lower frequency is superposed on the portion corresponding to the
high frequency power of the first high frequency apply means. It
follows that, even if the plasma sheath is affected by the standing
wave, the uniformity of the plasma is scarcely made poor, and the
plasma sheath of the lower electrode is made substantially uniform.
Therefore, it is possible to cope with the miniaturization
performed by a high density plasma, and it is also possible to
ensure a uniformity of the plasma processing by a uniform
plasma.
[0127] It should also be noted that, since the fluctuation in the
thickness of the plasma sheath is diminished by the application of
the high frequency powers to the first and second electrodes, the
intensity of the electric field in the sheath portion is kept
maintained at a value higher than a predetermined value. As a
result, the space potential of the plasma can be increased, and the
ionization rate can be increased so as to increase the plasma
density. It follows that the ions and the electrons are allowed to
have a high energy. It is also possible to increase the ionization
rate in the vicinity of the electrode so as to increase the high
speed electron flux. It follows that the electrons within the
plasma are allowed to reach easily the bottom portion of the
contact hole so as to neutralize the positive charge within the
hole. AS a result, the shading damage is unlikely to take
place.
[0128] As described above, the prominent effects described above
can be produced by applying high frequency powers substantially
forming reverse phases to the first and second electrodes. However,
desired effects can also be obtained if the phase difference
between the high frequency powers applied to the first and second
electrodes falls within a range of 180.+-.45.degree..
[0129] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *